First, about changing the display settings. If the game crashes when you change them, there is an external '
Game Settings' link located in the '
Tomb Raider - Legend [GOG.com]' directory in your Start Menu, and in it you can change most visual options before loading the game. I would suggest setting it to your desktop resolution and then go to the Video options (in game) and change
Widescreen to
On for a correct aspect ratio.
Second, about the random crashes. A good place to search about these things is PCGamingWiki
https://www.pcgamingwiki.com/wiki/Home and in their page for Tomb Raider: Legend there is a
Random Crashing section with a fix, but I haven't tried it. There are 2 versions of a fixed exe to download: Retail and Steam. I don't know if they would work with the GOG version, so make a backup of the original 'trl.exe' before trying them.
EDIT: Sorry, I couldn't post a proper link for the Tomb Raider: Legends page with the random crashing section.
EDIT 2: This GOG version probably has all the latest fixes, so I was wondering, do you have the '
Next generation content' turned
On in the game's advanced display settings?
Because I read that for some people it caused crashes at certain places during gameplay. Maybe you can try turning that option
Off.